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UniversityofLouisvilleUniversityofLouisvilleThinkIR:TheUniversityofLouisville'sInstitutionalRepositoryThinkIR:TheUniversityofLouisville'sInstitutionalRepositoryElectronicThesesandDissertations12-2012SynthesisandCO2/CH4separationperformanceofBio-MOF-1SynthesisandCO2/CH4separationperformanceofBio-MOF-1membranes.
membranes.
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"(2012).
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SYNTHESISANDCO2/CH4SEPARATIONPEFORMANCEOFBIO-MOF-1MEMBRANESByJosephAllenBohrmanB.
S.
Ch.
E.
,UniversityofLouisville,May2011AThesisSubmittedtotheFacultyoftheUniversityofLouisvilleJ.
B.
SpeedSchoolofEngineeringasPartialFulfillmentoftheRequirementsfortheProfessionalDegreeMASTEROFENGINEERINGDepartmentofChemicalEngineeringDecember2012iiSYNTHESISANDCO2/CH4SEPARATIONPEFORMANCEOFBIO-MOF-1MEMBRANESSubmittedby:JosephBohrmanAThesisApprovedOn(Date)bytheFollowingReadingandExaminationCommittee:Dr.
MoisesCarreon,ThesisDirectorDr.
YongshengLianDr.
GeroldWillingDr.
JamesWattersAPPROVALPAGEiiiACKNOWLEDGEMENTSIcannotexpresshowmuchgratitudeandpraiseIhaveforDr.
MoisesA.
Carreon,myadvisor.
Hiscontinuoussupportandguidancehelpedmereachthismilestone.
Withouthisunderstanding,incredibleknowledge,andmostimportantly,hisfriendship,Iwouldnothavebeenheretoday.
IwouldliketothankalsomyfamilyandfriendsfortheirmoralsupportwhenIwantedtothrowinthetowel.
TheirunyieldinglovegavemethemotivationanddriveIneededincontinuingthisjourney.
I'dliketoespeciallythankMinqiforherassistanceinthelab.
Westartedourresearchtogetherandbothgrewintothestudentswearetoday.
Iwillmissherfriendship.
IgivemuchgratitudetowardsMs.
PatriciaLumleyandDr.
JamesWattersfortheirworkinmakingthispossible.
Mycollegecareerhasbeenatwistedroadthatwaskeptstraightwiththeirmuchneededassistance.
Lastly,IwouldliketothankDr.
YongshengLianandDr.
Willingforsittingonmythesisdefensecommittee.
ivABSTRACTTheseparationofcarbondioxidefromnaturalgasisofgreatinterestfromtheenvironmentalandenergyperspective,respectively.
Fromtheenvironmentalpointofview,capturingCO2effectivelyfrompowerplantscanhaveapositiveimpactonreducinggreenhousegasemissions.
Fromtheenergypointofview,CO2isanundesirableimpurityinnaturalgaswells,withconcentrationsashighas70%.
Membranetechnologycanplayamajorroleinmakingnaturalgaspurificationprocesseseconomicallyfeasible.
AnovelmembranecomposedofMetal-organic-frameworkmaterialZn8(Ad)4(BPDC)6O2Me2NH2(Bio-MOF-1)wasdesignedandcreatedtoeffectivelyseparateCO2/CH4gasmixtures.
Thecrystallinestructure,composition,andtexturalpropertiesofBio-MOF-1membraneswereconfirmedthroughx-raydiffractometry,CHNanalysis,transmissionelectronmicroscopy,adsorptionmeasurementsandBETsurfacearea.
Asecondaryseededgrowthapproachwasemployedtopreparethesemembranesontubularstainlesssteelporoussupport.
ThesemembranesdisplayedhighCO2permeances(11.
5x10-7mol/m2sPa)andmoderateCO2/CH4separationselectivities(1.
2-2.
5).
TheobservedselectivitiesareabovetheKnudsenselectivityandindicatethattheseparationispromotedbypreferentialCO2adsorptionoverCH4.
ThispreferentialadsorptionisattributedtothepresenceofadeninateaminobasicsitespresentintheBio-MOF-1structure.
Theworkdemonstratedshowsthefeasibilityofthedevelopmentofanoveltypeofmembranethatcouldbepromisingfordiversemoleculargasseparations.
vTABLEOFCONTENTSAPPROVALPAGE.
iiACKNOWLEDGEMENTS.
iiiABSTRACT.
ivNOMENCLATURE.
viLISTOFTABLESviiLISTOFFIGURESixI.
INTRODUCTION1A.
EnvironmentalandEnergyConcernsforCarbonDioxide.
11.
GreenhouseGasEmissionsandaRisingConcern.
12.
NaturalGasasanAlternativeFuelSourceandAssociatedChallenges.
23.
CurrentSeparationMethodsandaShifttoGreenTechnologies3B.
GaseousMixtureSeparationsUtilizingNanoporousMaterialMembranes51.
WhatareMetal-OrganicFrameworks52.
HowdoMOFsdifferfromBio-MOFs73.
BackgroundandResearchonBio-MOF-1.
8C.
Justification9D.
Objectives.
10II.
EXPERIMENTATION.
11A.
SynthesisofBio-MOF-111B.
Bio-MOF-1Characterization12C.
Bio-MOF-1MembranePreparationandTesting.
13D.
Equipment151.
SynthesisofBio-MOF-1.
152.
Bio-MOF-1Characterization.
173.
Bio-MOF-1MembraneTesting.
19III.
RESULTSANDDISCUSSION20A.
CharacterizationofBio-MOF-120B.
MembraneSeparationPerformance24IV.
CONCLUSIONS.
29V.
RECOMMENDATIONS.
31A.
SynthesisofBio-MOF-131B.
CharacterizationofBio-MOF-131C.
SeparationPerformanceofBio-MOF-131REFERENCESCITED33APPENDIX35VITA.
39viNOMENCLATUREAd=adenine=angstroma.
u.
=arbitraryunitatm=atmosphereBPDC=4,4'-biphenyldicarboxylicacidBET=BrunauerEmmettTellerCO2=carbondioxideCHN=Carbon,Hydrogen,NitrogenoC=CelsiusCu=Coppercm3=cubiccentimeterDEA=diethanolamineθ=diffractionangle(degree)DMF=N'N-dimethylformamided=d-spacing(Angstrom)GC-MS=gaschromatograph–massspectrometryTg=glasstransitiontemperature(Celcius)g=gramhr=hourH2S=hydrogensulfiden=integerKα=K-alphax-raysK=kelvinKPa=kilopascalkV=kilovoltP/Po=measuredpressure/saturationpressureMg=megagramMW=megawattBio-MOF=metal-biomoleculeframeworkMOF=metal-organicframeworkCH4=methaneMDEA=methyldiethanolaminem=micrometermA=milliampmL=millilitermmol=millimoleMMBtu=millionmetricbritishthermalunitsMMT=millionmetrictonmin=minuteviiMEA=monoethanolamineHNO3=nitricacidPPM=partspermillionPa=pascalPEI=polyethleniminePi=permeanceofspeciesi(mol/m2sPa)RPM=revolutionsperminuteSEM=scanningelectronmicroscopys=secondm2=squaremeterTR=thermallyrearrangedTGA=thermogravimetricanalysisTEM=transitionelectronmicroscopyH2O=waterλ=wavelength()XRD=x-raydiffractometryZn(O2CCH3)2(H2O)2=zincacetatedehydrateZn4O=zincoxideclustersZnO4=zincoxidetetrahedraviiiLISTOFTABLESTABLEI-CO2/CH4separationperformanceofBio-MOF-1membranesattrans-membranepressuredropof138KPaand298K27TABLEII–BETTabularResultsforBio-MOF-1Seeds35TABLEIII–BETTabularRestulsforBio-MOF-1MembraneCrystals.
37ixLISTOFFIGURESFIGURE1–CO2EmissionsintheUSbySectorandFuel(inMMT)1FIGURE2–ProcessFlowDiagramofNaturalGasAlkanolamineTreatment.
4FIGURE3–ConventionalMembraneTechnologyforGasSeparation4FIGURE4–CubicTopologyofMOF-5.
6FIGURE5–PorosityofMOFsComparedtoZeolites.
7FIGURE6–AdenineMoleculeDisplayingMultipleBindingSites8FIGURE7–StructuralFeaturesofBio-MOF-1Columns(Left)andInterconnectedColumns(Right)9FIGURE8–Bio-MOF-1CrystalSynthesis.
12FIGURE9–Bio-MOF-1MembraneSynthesis13FIGURE10–GasSeparationSystemSchematic14FIGURE11–HydrothermalAutoclavewith50mLTeflonVessel15FIGURE12-NeyVulcan3-550Furnace15FIGURE13–EppendorfCentrifuge.
16FIGURE14–PrecisionVacuumOven.
17FIGURE15–X-RayDiffraction.
17FIGURE16–MicromeriticsTristar3000Porosimeter18FIGURE17–NovaNanoSEM600.
18FIGURE18–StainlessSteelHighPressureGasSeparationSystem19FIGURE19–GC-MS19FIGURE20–XRDPatternofBio-MOF-1.
21FIGURE21–SEMSurfaceMorphologyofTwoPhaseBio-MOF-1Crystals(Left)andPureNanobarBio-MOF-1Crystals22FIGURE22–Bio-MOF-1AdsorptionProperties.
23FIGURE23–TEMandDiffractionPatternsforBio-MOF-1Seeds24FIGURE24–SEMImagesofBio-MOF-1MembraneandSurfaceMorphology:TopView(Left)andCross-Section(Right)25FIGURE25–XRDPatternofBio-MOF-1Membrane(M1)26FIGURE26-RobesonPlotforCO2/CH4Mixtures…28FIGURE27-BETIsothermsforBio-MOF-1Seeds…36FIGURE28-BETIsothermsforBio-MOF-1MembraneCrystals…381I.
INTRODUCTIONA.
EnvironmentalandEnergyConcernsforCarbonDioxide1.
GreenhouseGasEmissionsandaRisingConcernSincetheindustrialrevolution,humaninvolvementhasbeenincreasinglyaddingtotheamountofcarbondioxideintheatmospherefrom280to360PPM1.
Inthepast250years,theatmosphericlevelofcarbondioxidehasrisenbyaround31%2.
Carbondioxidecontributesto60%ofthegreenhousegasesthatcauseglobalwarming1.
Figure1showsthedistributionofCO2emissionsamongdifferentUSsectorsbyfuelsource.
In2000alone,CO2emissionsaccountedfor83%oftotalU.
S.
greenhousegasemissions3.
FIGURE1–CO2EmissionsintheUSbysectorandfuel(inMMT)32Asthesegases,especiallyCO2,continuetoincrease,potentialadverseeffectsonregionalandglobalclimate,ecosystemfunction,andhumanhealthincreaseaswell.
Inanefforttoreducetheseemissions,manynationalgovernmentsarelookingtointroducemandatoryreportingofgreenhousegasemissions.
AsrecentlyasJuly2009,a1,200page2climate-changeandenergybill(H.
R.
2454)madeitswaythroughCongressinordertoestablisha"capandtrade"systemtoreducecarbondioxideemissions4.
Thebillwouldcutemissionsby17%of2005levelsby2020andby83%of2005levelsby20504.
ReportingemissionsusingthresholdsisalsopartofeffortsintheEUandCanadatomonitorgreenhousegasemissions.
TheOntarioMinistryoftheEnvironment(MOE)currentlyhasamandatoryemissionsmonitoringandreportingprogramthatrequiresfacilitiestoreportifemissionsexceed100,000MgofCO25.
Althoughstepsaroundtheglobehavebeeninitiatedtoquellthesituation,worldenergy-relatedCO2emissionswillincreasebyapproximately40%by2040accordingtocurrentprojectedrates4.
2.
NaturalGasasanAlternativeFuelSourceandAssociatedChallengesCoincidingwiththegrowingconcernofatmosphericCO2concentrationsisworldenergydemands.
Fossilfuelsaccountforapproximately80%oftheworldwideenergydemandwhichproducesCO26.
Inanefforttoreducefossilfuelenergyproduction,researchisbeingdirectedtowardsalternativefuels,carboncapture,andcarbonsequestration.
Withtheemergenceofthesenewtechnologies,estimatessuggestthatU.
S.
naturalgasreserveshavedoubledandgaspriceshavedroppedfromahighof$15/MMBtuin2006tolessthan$3/MMBtuinearly20127.
Lowcostscombinedwithanabundanceofsupplymakesnaturalgascombustionturbineslookextremelyattractiveforelectricitygeneration.
U.
S.
powergenerationfromnaturalgasgrewfrom14%in1997to23%in20107.
NaturalgaspowerplantsprovidemanyadvantagesincludinghigherefficiencyandlowersulfurandCO2emissionsperMWgenerated7.
IfCO2emissionsbecomeheavilyregulated,ashifttowardsnaturalgaspowerplantswillaccelerateinthefuture.
3Inordertoeffectivelyusenaturalgasasafuelsource,thefuelsupplymustbepurifiedofanyimpuritiestoincreaseitsenergycontent.
Carbondioxideisanundesirableimpurityinnaturalgaswells,withconcentrationsashighas70%8.
Inadditiontoloweringtheenergycontentofnaturalgas,carbondioxideisacidicandcorrosiveinthepresenceofH2O.
CurrentpipelinespecificationsrequireaCO2concentrationbelow2-3%9.
3.
CurrentSeparationMethodsandaShifttoGreenTechnologiesThemostwidelyusedprocesstopurifynaturalgasutilizesalkanolamineaqueoussolutiontoabsorbselectivelyCO2andH2Sfromnaturalgasstreams10.
Themostcommonlyusedaminesinindustrialplantsarethealkanolaminesmonoethanolamine(MEA),diethanolamine(DEA),andmethyldiethanolamine(MDEA),allofwhichareharmfultotheenvironmentandhumanhealth11.
Thisprocessisextremelyenergyintensiveandrequiresmultiplestepsinpreparationfortheseparationandsolutionrecovery(heatingofthesolution,recoveryofacidgases,etc.
).
Figure2displaysacommonschematicforanalkanolaminetreatingprocessfornaturalgaspurification.
4FIGURE2–ProcessFlowDiagramofNaturalGasAlkanolamineTreatment11Inanefforttoreducethehighenergyconsumption,chemicalsinvolved,phasechanges,complexequipment,andpronenesstopollution,membranetechnologyisbeingincreasinglyadoptedintheindustry12.
Ratherthansubjectthefeedgasstreamtomultiplesteps,asimple,pressuredrivendesignwouldpromotetheseparationofCO2fromCH4.
FIGURE3–ConventionalMembraneTechnologyforGasSeparation13Figure3showsthistechnologywhereagaseousmixture(inthiscaseCO2/CH4)wouldenterthetubularsupportfromtheleftandtheCO2wouldpermeatethroughthewallswhiletheremainingCH4wouldexitthesupport.
Polymericmembraneshavebeen5theindustrystandardforseparationbecauseoftheircompetitiveperformanceaswellastheirlowmanufacturing/productioncosts14.
Forgaseousseparations,nonporousmembranesareused.
Thevaporsandgasesareseparatedbytheirdifferenceinsolubilityanddiffusivityinthepolymers15.
Smallmoleculesmoveamongthepolymerchainsaccordingtotheformationoflocalgapsbythermalmotionofpolymersegments.
PorousmembranesrelysolelyontheKnudsendiffusionfortheseparationofgaseousmixtures15.
B.
GaseousMixtureSeparationsUtilizingNanoporousMaterialMembranes1.
WhatareMetal-OrganicFrameworksWhilepolymericmembranesarehighlysoughtafterfortheirlowmanufacturing/productioncostsandhighperformance,theydohaveweaknesses.
Plasticizationisacommonoccurrenceforpolymericmembranes.
WiththesorptionofCO2,polymersswellandchangeinmechanicalandphysicalproperties.
Themostimportantoftheseisthereductionoftheglasstransitiontemperature(Tg),simplycalledplasticization16.
TheCO2moleculesinteractwiththebasicsitewithinthepolymerandreducechain-chaininteractions.
Thisreductionincreasesthemobilityofpolymersegmentsthusreducingtheglasstransitiontemperature(Tg).
Plasticizationcausesthermalinstabilityandcanleadtofracturingofthepolymericmembrane16.
Materialsthatareabletowithstandharshconditions(thermallyandchemicallystable)whileabletoadsorblargeamountsofCO2(highsurfaceareas)areneededforthepurificationofnaturalgas.
Afamilyofmaterialsthatareabletoprovideeachofthesecharacteristicsismetal-organicframeworks(MOFs).
MOFsarecrystallinecompoundsconsistingofmetal6ionsorclusterscoordinatedtooftenrigidorganicmoleculestoformthree-dimensionalporousstructures.
Figure4displaystheprototypicalmetal-organicframeworkMOF-520.
FIGURE4-CubicTopologyofMOF-517MOF-5isbuiltupbyZn4Ogroupsonthecornersofacubiclattice,interconnectedbyterephthalicacidligands.
ZnO4tetrahedra(polyherda)arejoinedbybenzenedicarboxylatelinkers(OandC)creatingporeaperturesof8Angstromsanda12Angstromporediameter(sphere).
MOF-5hasthermalstabilityupto400°Candahighsurfaceareaof2900m2g-118.
Comparedtozeolites,anotherfamilyofwell-knownmaterialsusedintheseparationofgaseousmixtures,MOFshaveamuchlargerdiversityinporosityallowingforabroadrangeofapplicationssuchcatalysis(largeporediameter/volume)andespeciallygasseparations(smallporediameter/volume).
Figure5comparesseveralMOFS(dotsandsquares)toafewzeolites(diamonds)tovisuallydisplaythediversitywithinthisfamilyofmaterials.
7FIGURE5–PorosityofMOFSComparedtoZeolites192.
HowdoMOFsdifferfromBio-MOFsTheabilityofMOFstobecarefullytailored,coupledwiththeirdiverseapplications,makesthemoneofthemostgrowingareasofresearch.
NewgenerationsofMOFSarebeingdesignedtobecompatiblewiththeenvironmentandhumanbody20.
Toaccomplishthistask,biomoleculesareincorporatedintheconstructionofMOFsasligands,asopposedtotraditionalorganicligand(imidazole,etc.
).
ThissubsetofmaterialsintheMOFfamilyisknownasBio-MOFs.
Withtheintroductionofbiomoleculesasligands,additionaladvantagesareintroducedsuchasstructuraldiversity(rigidorflexible)whichimpactsthefunctionalnatureoftheBio-MOF,aswellashighCO2adsorptioncapacity20.
ThebiomoleculesavailablefortheconstructionofBio-MOFscanbecategorizedwithinoneoffivegroups:aminoacids,peptides,proteins,nucleobases,andsaccharides(carbohydrates).
Eachgroupofbiomoleculesprovidesexcellentligands.
However,8nucleobases(keyconstituentofnucleicacidswhichisinvolvedinbase-pairing)maketheidealbio-linkers20.
NucleobaseshaveH-bondingcapabilitiesandmultiplenitrogenelectronlonepairswhichallowsforrichbindingsites(multidentate).
Ofthewiderangeofnucleobasesexisting,adenine(Figure6)hasbeenthemostreported20.
Adenineoffersfivebindingsites,eachlocatedatanaminogroup.
FIGURE6–AdenineMoleculeDisplayingMultipleBindingSites213.
BackgroundandResearchonBio-MOF-1Thefirstthree-dimensionalpermanentlyporousframeworkusingadeninetoderiveaBio-MOFwasZn8(Ad)4(BPDC)6O·2(NH2(CH3)2)+,8DMF,11H2O,alsoknownasBio-MOF-120.
Bio-MOF-1consistsofZn(II)-Adeninatecolumncomposedofoctahedralcageswitheachcageconsistingof8Zn2+cationswith4adeninatelinkers,Figure722.
9FIGURE7–StructuralFeaturesofBio-MOF-1,Columns(Left)andFramework(Right)22Eachcolumnisinterconnectedviabiphenyldicarboxlyateformingatetragonallatticecrystalsystemwithporeaperturesofapproximately5.
2Angstroms.
NitrogenadsorptionstudiesrevealedthatBio-MOF-1hasaBETsurfaceareaof1700m2g-1.
Thermogravimetricanalysis(TGA)revealedadecompositiontemperatureofapproximately300oC22.
C.
JustificationBio-MOF-1possessessomehighlyappealingpropertiesthatarenecessaryfortheseparationofCO2fromCH4inanefforttopurifyingnaturalgaswells.
Thebiomoleculeadenineusedasaligandprovidesrichbindingsitesforcarbondioxideadsorption.
OtherpromisingpropertiesofBio-MOF-1includehighsurfacearea,thermalstability,andchemicalstability.
10D.
ObjectivesTheobjectivesofthecurrentstudyareto:1)DevelopBio-MOF-1crystalsdisplayingnarrowsizedistributionandenhancedCO2adsorptionproperties.
2)DevelopreproducibleandcontinuousBio-MOF-1membranesforCO2/CH4separation.
3)Establishbasicstructure/separationrelationshipsofBio-MOF-1membranesinrelevantfunctionalgasseparationsrelatedtonaturalgas.
11II.
EXPERIMENTATIONA.
SynthesisofBio-MOF-1Thezinc-adeninatemetal-organicframeworkBio-MOF-1wassynthesizedsimilarlytothemethoddescribedbyRosi'sgroup22.
Inatypicalsynthesis,showninFigure8,0.
25mmolofAdenine(C5H5N5,SigmaAldrichInc.
,≥99.
0%),0.
5mmolof4,4'-biphenyldicarboxylicacid(BPDC,HO2CC6H4C6H4CO2H,SigmaAldrichInc.
,97%),and0.
75mmolofzincacetatedihydrate(Zn(O2CCH3)2(H2O)2,SigmaAldrichInc.
,≥99%)weredissolvedinamixtureof2mmolofnitricacid(HNO3,SigmaAldrichInc.
,≥90.
0%),2mLofdeionizedwater,and13.
5mLofN,N-dimethylformamide(DMF,HCON(CH3)2,AcrosOrganics,99.
8%).
Tofacilitatethedisolution,thesolutionwasvigorouslystirredfor30minutesat300RPM.
Thepreparedgelsolutionwaspouredintoa50mLTeflonvessel.
Eachvesselwasplacedintoanautoclavetoallowthesolutiontoreachanautogenouspressureasheated.
Theautoclavewasplacedintoaprogrammableovenwitha1oC/minrampupfromroomtemperatureto130°Cfor24hours.
Rod-shapedcolorlesscrystalsobtainedaftersynthesiswereseparatedfromtheeffluentbycentrifugationat3000RPMandwashedthreetimeswith3mLofDMF.
TheresultingcrystalswerethenplacedinaPrecisionvacuumovenandsubjectedtodryinginanargonatmosphereatatemperatureof125°Cfor2hours.
12FIGURE8–Bio-MOF-1CrystalSynthesisB.
Bio-MOF-1CharacterizationTheresultingcrystalswerethencharacterizedusingX-raydiffraction,scanningelectronmicroscopy,transmissionelectronmicroscopy,CHNanalysisandBETsurfacearea.
ThepowderX-raydiffractionpatternsweregatheredbyuseoftheBrukerD8-Discoverdiffractometer,Figure15,at40kV,40mAwithCuKαradiation.
TheBETsurfaceareameasurementsweretakenonaMicromeriticsTristar3000porosimeterwhichoperatedat77Kusingliquidnitrogenascoolant.
Thesamplesweredegassedat130°Cforthreehoursdirectlybeforebeingplacedintheporosimeter.
ThescanningelectronmicroscopywasperformedusingaFE-SEM(FEINova600)withan13accelerationvoltageof6kV.
Thequantitativeanalysisofelementalcarbon,hydrogen,andnitrogenwerecarriedoutatMidwestMicrolab,LLC(Indianapolis).
C.
Bio-MOF-1MembranePreparationandTestingBio-MOF-1membraneswerepreparedviasecondaryseededgrowthinsidetubularporousstainlesssteelsupports(0.
1grade,0.
27mpores,MottCorporation),Figure9.
ThesynthesissolutionpreparationandcompositionissimilartothatuseforthesynthesisofBio-MOF-1seeds.
ThemembraneswerepreparedbyrubbingtheinsidesurfaceofporoussupportswithdryBio-MOF-1seedsusingcottonswabs.
Therubbedporoussupports,withtheiroutsidewrappedinTeflontape,werethenplacedverticallyina50mLTeflonautoclaveandfilledwiththesynthesissolution.
Thereactionwascarriedoutatthesameconditionsforseedsynthesis(130oCfor24hours)intheNeyVulcan3-550Furnace.
TheresultingmembranesweregentlywashedwithDMFnotonlytorinsethemembrane,butalsoremoveexcessbuildupofcrystalswithinthetubularsupport.
Multiplelayerswereappliedfollowingthesameprocedure.
Themembranesweredriedat100oCunderanargonatmospherewithinthePrecisionVacuumOven.
FIGURE9–Bio-MOF-1MembraneSynthesisTheseparationperformanceoftheBio-MOF-1membranesforequimolarCO2/CH4gasmixturewasmeasuredinaseparationsystemshowninFigure10.
ThemembranesweremountedinastainlesssteelmodulewithsiliconeO-ringsassealson14bothends.
Thedrivingforceacrossthemembranewasprovidedbyapressuredropof138KPawiththepermeatepressurebeing99.
5KPa(atmospheric).
Thepermeategasratewasmeasuredbyasoapfilmbubbleflowmeter.
Thetotalflowratewas100mL/min.
Thecompositionsofthefeed,retentate,andpermeatestreamsweremeasuredusingagaschromatograph(SRIinstruments,8610C)equippedwithathermalconductivitydetectorandHAYESEP-Dpackedcolumn,Figure19.
Theoven,injectoranddetectortemperaturesintheGCwerekeptat65oC,100oCand150oCrespectively.
FIGURE10–GasSeparationSystemSchematic15E.
Equipment1.
SynthesisofBio-MOF-1FIGURE11-HydrothermalAutoclavewith50mLTeflonVesselFIGURE12-NeyVulcan3-550FurnaceDentsupplyCeramcoInternationalSerialNo.
:9493308York,PA1740416FIGURE13-EppendorfCentrifugeModelNo:5702SerialNo:5702YN32098917FIGURE14-PrecisionVacuumOvenModelNo.
:29SerialNo.
:69902505Winchester,VA226022.
Bio-MOF-1CharacterizationFIGURE15-X-RayDiffraction,BrukerAXS–DiffraktometerD8SerialNo.
:203407Karlsruhe,GermanyD761812318FIGURE16-MicromeriticsTristar3000PorosimeterFIGURE17-NovaNanoSEM600FEI24193.
Bio-MOF-1MembraneTestingFIGURE18-StainlessSteelHighPressureGasSeparationSystemModelNo:4576AFIGURE19-GC-MSHP5890GasChromatographequippedwith5970MassSelectiveDetector20III.
RESULTSANDDISCUSSIONA.
CharacterizationofBio-MOF-1ThemethodprovidedbyRosiwasfollowedcloselytocreateBio-MOF-122.
Severalsamplesweresuccessfullycreatedusingthismethod,eachofapproximately0.
1gofproduct.
Thisyieldedthecorrectcrystallinestructure,withthepowderX-raydiffractionpatternmatchingcloselythatshowninFigure20.
TherelativeintensityandpeakpositionsoftheXRDpatternareinagreementwiththetypicalstructureofBio-MOF-122.
SomeofthesecondarypeakswerebroaderandlessintensethanthereportedXRDpatternofBio-MOF-1fromRosi'sgroup,indicatingthatalthoughtheBio-MOF-1crystalsmaintainedlong-rangecystallinity,itsframeworkmayhaveagreaterdegreeoflocalstructuraldisorder.
Localstructuraldistortionshavebeenassociatedwithsurfacerelationeffectsand/orthepresenceofextendedstructuraldefects25.
21FIGURE20–XRDPatternofBio-MOF-126ScanningelectronmicroscopyimagesofBio-MOF-1crystalscanbeseeninFigure21.
Thesampleshownontheleftdisplaystwophases,ananobarcrystallinephaseandanamorphoussphericalphase.
ThepresenceoftheamorphousBio-MOF-1phasesuggeststhatthenecessarysynthesisreactiontimehadnotbeenmet.
Thesampleontherightdisplayswell-definednanobarswithlengthsrangingfrom0.
5-4.
5mandwidthsfrom0.
05-0.
15mwereobserved26.
Theuniformsurfacemorphologyandcrystalsizesuggeststhatmembraneformationispossibleduetoexcellentpacking.
Excellentpackingisimperativeinmembraneformationinthereductioninnonselectivepathways.
22FIGURE21–SEMsurfacemorphologyoftwophaseBio-MOF-1crystals(Left)andpurenanobarBio-MOF-1crystals(Right)26TheapparentBETsurfaceareaoftheBio-MOF-1crystalswasapproximately800m2g-1.
Whilethisvalueismuchlowerthanpreviousreports22,20,thelowersurfaceareamayberelatedtotheincompleteremovalofdimethylammoniumcations,DMFortowaterresidingintheporesofthestructureand/ortotheextentoflocaldisorderintheframeworkasnotedfromtheXRDpatterninconsistencies26.
Attemptstoremovethesemoleculesbysolventexchange(chloroform,methanol,etc.
)resultedintheframeworkcollapsing.
OthervaryingdryingmethodswereattemptedinopeningtheBio-MOF-1frameworksuchasundervacuum(20inHG)andatvaryingtemperatures,however,allattemptsagainledtotheframeworkcollapsing.
CHNanalysisrevealedthatthecarbon,hydrogen,andnitrogencontentsoftheBio-MOF-1frameworkwereC-46.
6%,H-3.
9%,andN-11.
7%26,whichagreewiththecalculatedtheoreticalamountsofC-46.
7%,H-4.
7%,andN-12.
3%22.
TheadsorptionisothermsatlowP/PorelativepressureofCO2andCH4forBio-MOF-1werecollectedatroomtemperature.
Figure22showsthatBio-MOF-1crystalspreferentiallyadsorbedCO2overCH4.
AtP/Poapproximately0.
04,thecrystalsadsorbed9timesmoreCO2thanCH4reaffirmingtheirappealingnatureforCO2separationfromothergases26.
Thispreferential23adsorptioncanbeattributedtothepresenceofadeninateaminobasicsiteswithintheporousframework26.
FIGURE22–Bio-MOF-1CO2andCH4adsorptioncapacities26Transmissionelectronmicroscopy(TEM)wasemployedasanadditionalmeansofcharacterizingthesynthesizedseeds.
Figure23showstheTEMimagesoftwonanobarsselectedfromthecrystallinesampleshowninFigure21.
BeloweachTEMimagesisthevisualdiffractionpatternpresentingthespacingbetweenparticularcrystalplanes.
CO2CH424FIGURE23–TEMandDiffractionPatterns(Left)andXRDPattern(Right)forBio-MOF-1SeedsUtilizingBragg'slaw27,thed-spacingscalculatedagreewellwiththosefoundthroughtheTEManalysisasindicatedintheXRDpatterninFigure23.
Wherenisaninteger,isthewavelengthoftheincidentwave,disthespacingbetweentheplanesintheatomiclattice,andistheanglebetweentheincidentrayandthescatteringplanes.
B.
MembraneSeparationPerformanceAsdescribedinBio-MOF-1membranepreparationandtesting,thesecondaryseededgrowthapproachwasemployedtopreparethemembranes.
Thismethodprovidesnucleationsitesformembranegrowthaswellaseliminatesgapsinbetweentheparticlesthroughtheadditionofmultiplelayers.
Eliminationoccurseitherthroughattachmentofnewlyformedcrystalsorbythegrowthofthecrystalsalreadypresentonthe25membrane26.
Figure24presentsSEMimagesobtainedofthetopviewaswellasthecrosssection.
FIGURE24–SEMimagesofBio-MOF-1MembraneSurfaceMorphology:Topview(Left)andCross-Section(Right)26TheBio-MOF-1membranesurfaceandcrosssectionalviewsdisplaythesamenanobarcrystalmorphologyasseenpreviouslyinthesynthesizedseeds(Figure21).
Lengthsinthe~9-11mrangeandwidthsinthe~1-2mrangewereobserved.
Theincreaseinsizeisrelatedtotherecrystallizationandgrowthofthecrystalswiththeincorporationofmultiplelayers26.
Thepreferentialperpendiculargrowthdirectionsuggestsanepitaxialgrowthmechanism26.
Thethicknessofthisparticularmembranewas~15m.
TheXRDpatternofthemembranecorrespondstothestructureofBio-MOF-1,Figure25.
26FIGURE25–XRDPatternofBio-MOF-1Membrane(M1)Thedifferenceinpeakintensity,betweenthemainpeakandsecondarypeaks,ascomparedtotheXRDpatternoftheseeds,Figure20,mayindicatethepreferentialorientationofthecrystals.
ThisbehaviorhasbeenobservedinotherMOFfilms28.
TheCO2/CH4separationperformanceofthestainlesssteelsupportedBio-MOF-1membranesisshowinTable1.
Atleast3layerswereneededtoobtaincontinuousmembranes.
MembranesM1andM2werepreparedwiththreelayers,M3with4layers,andM4with7layers.
CO2permeancesashighas11.
9x10-7mol·m-2s-1Pa-1andCO2/CH4selectivitiesof2.
6wereobserved26.
MembranereproducibilitywasconfirmedbythesimilarseparationperformancesofM1andM2.
TheadditionofmultiplelayerscorrelatedwithadecreaseinCO2permeanceandCO2/CH4selectivity.
27TABLEICO2/CH4SEPARATIONPERFORMANCEOFBIO-MOF-1MEMBRANESATTRANS-MEMBRANEPRESSUREDROPOF138KPAAND298K26.
MembraneaPCO2(x10-7)mol/m2·s·PaPCH4(x10-7)mol/m2·s·PaCO2/CH4selectivityM1(3)11.
54.
62.
5M2(3)11.
94.
62.
6M3(4)10.
54.
82.
2M4(7)5.
84.
71.
2a)NumbersinparenthesisindicatenumberoflayersThedecreaseinCO2permeanceisduetoanincreaseinmembranethickness.
TheadditionofmorelayersresultsinanincreaseofBio-MOF-1pores(selective)andnon-Bio-MOF-1pores(non-selective)26.
TheselectivetransportpathwaysforCO2areaconsequenceofthebasicadeninatesites.
Thenon-selectivepathwaysassociatewithintercrystallineboundariesand/oramorphousregions,sincetheseporesdifferinsizeandadsorptionpropertiescomparedtotheselectivepathways.
Therefore,thedecreaseinCO2/CH4selectivitysuggeststheadditionofmorelayersresultsinahigherconcentrationofnon-selectivepathways26.
TheobservedCO2/CH4selectivitiesaregreaterthan0.
6suggestingthatthemainmechanismofseparationispreferentialadsorptionofCO2overCH4andnotKnudsenselectivity29.
Again,thisissupportedbyFigure22whichshowsthattheCO2adsorptioncapacitiesofBio-MOF-1crystalsarehigherthanthatofCH4.
TheRobesonplotforCO2/CH4separationselectivitiesasafunctionofCO2permeabilities(permeancexmembranethickness)ofpolymericmembraneshasbeenwidelyusedtocomparetheperformanceofmembranes30.
Forcomparison,theseparationperformanceforBio-MOF-1membraneM1hasbeenincludedinthisplot,showninFigure26.
28FIGURE26–RobesonPlotforCO2/CH4Mixtures30ThedatapointfortheBio-MOF-1membraneliesintheregionofconventionalpolymericmembranes.
Althoughitsseparationperformanceislowerthanthatofthermallyrearranged(TR)polymericmembranesandmostzeoliticmembranes,itliesattheupperextremitiesforCO2permeances31.
FurtheroptimizationofsynthesisandprocessingparametersduringthepreparationofthesemembranescouldpotentiallyleadtomoreCO2selectivemembranesandultimatelyextremelycompetitiveandsoughtaftermembranes.
29IV.
CONCLUSIONSBio-MOF-1crystalsweredevelopedfollowingthepresentedmethodsbyRosi22.
ComprehensivecharacterizationtechniqueswereusedtostudythetexturalandmorphologicalpropertiesofthegeneratedBio-MOF-1.
TEM,CHNanalysis,andXRDallconfirmedthesynthesizedmaterialwasindeedBio-MOF-1.
LocalstructuraldisorderwasobservedfromtheobtainedXRDpatternsbynoticingthebroaderandlessintensesecondarypeaks.
ThecrystalsobtaineddisplayedaBETsurfaceareaof~800m2g-1.
Thisvalueisonlyhalfofthatreported22andcanbeattributedtodimethylammoniumcations,DEFsolvent,andwaterremainingwithintheframework.
Furtherattempts(solventexchange,vacuumdrying,etc.
)failedtovacatetheBio-MOF-1pores.
ScanningelectronmicroscopywasalsoperformedontheBio-MOF-1crystals,previouslyunreported.
TheSEMimagesrevealnanobarshapedparticlesoflengthrangingfrom0.
5-4.
5mandwidthfrom0.
05-0.
15m.
AdsorptionisothermswereacquireddisplayingCO2adsorbed9timesmorethanCH4reaffirmingtheirappealingnatureforseparation.
ThepreparationofcontinuousandreproducibleBio-MOFmembraneswasdemonstratedforafunctionalgasmixtureseparationforthefirsttime.
Themembraneswerepreparedviasecondaryseededgrowthontubularporoussupports.
Atleast3layerswereneededtoobtaincontinuousmembranes.
ThereproducibilitywasconfirmedbythesimilarseparationperformanceofM1andM2membranes.
ThesemembranesdisplayedhighCO2permeances(11.
5x10-7mol·m-2s-1Pa-1)andseparationabilityforCO2/CH4gasmixtures.
TheobservedCO2/CH4selectivites(2.
5-2.
6)wereabovetheKnudsen30selectivityindicatingthattheseparationispromotedbypreferentialCO2adsorptionoverCH4.
ThispreferentialCO2adsorptionwasattributedtothepresenceofadeninateaminobasicsitesintheBio-MOF-1structure.
TheadditionofmorelayersresultedinadecreaseinCO2permeanceandCO2/CH4selectivity.
Thedecreaseinseparationperformancewasrelatedtotheincreaseinconcentrationofnon-selectivepathways.
SEMimagesofthemembranerevealedintergrownbunchesofnanobarcrystalscoveringthesurfaceofthesupport.
Lengthsinthe9-11mrangeandwidthsinthe1-2mwereobserved.
Theincreaseinsizeandpreferredgrowthdirectionsuggestepitaxialgrowth.
31V.
RECOMMENDATIONSA.
SynthesisofBio-MOF-1DifficultieswereencounteredwithrepeatabilityinthesynthesisofhighsurfaceareaBio-MOF-1.
Variousotherchemicalscouldbeutilizedinthesolventexchangesuchasacetone,ethanol,andtolueneinhopesofvacatingtheporousframework.
DifferentBio-MOF-1compositionsneedtobeexploredaswellasdifferentparameterssuchasinorganicprecursors,synthesistime,andtreatmenttemperature.
Eachofthesecouldresultinthereductioninlocalstructuraldisorderandthusincreasingthestabilityoftheframeworkforsolventremoval.
B.
CharacterizationofBio-MOF-1AdditionalcharacterizationtechniquescanbeusedtoinvestigatetheBio-MOF-1crystalandmembraneframework.
ItwouldalsobehelpfultorunacomparativeTGAonthecrystalswithrespecttothepublishedliterature.
Thethermalstabilityofthecrystalsmayhavedecreasedduetothelargeamountofstructuraldisorder,thusleadingtothecollapseoftheframeworkduringdryinganddrasticallyreducingthesurfacearea.
C.
SeparationPerformanceofBio-MOF-1FutureexperimentsofBio-MOF-1membranesynthesisshouldfocusonemployingdifferentseedingtechniquesinanefforttopreparemorerobust,continuousmembranes.
Thesecondaryseededgrowthmechanismprovidesnucleationsites;32however,wherevertherearevacancieslocatedonthetubularsupport,theseedscannotestablishgrowth.
ByemployingamethodutilizingaPEI(polyethylenimine)solution,anchoringofBio-MOF-1seedstotheentiresurfaceispossibleremovingthechancefornon-selectivepathways,invariablyincreasingtheseparationperformance.
Asstatedpreviously,severalofthesynthesisparameters(gelcomposition,treatmenttimeandtemperature)canbeexploredduringmembranesynthesis,coupledwithseedingmechanisms,toincreasetherobustnatureofthemembrane.
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Report#:DOE/EIA–0383(2009)Appendix35TABLEIIBETTABULARRESULTSFORBIO-MOF-1SEEDSRelativePressure(P/Po)QuantityAdsorbed(cm/gSTP)RelativePressure(P/Po)QuantityAdsorbed(cm/gSTP)0.
085284884101.
04163460.
988505632202.
40639940.
141860462104.
00012330.
973981437196.
69113980.
201808211106.
25017950.
958531702189.
83801220.
241422118107.
56434030.
940030582183.
66179380.
299912856109.
22795860.
924635831179.
63403940.
349478361110.
56496830.
906950282175.
45400020.
447326429112.
97011760.
876976432169.
87071060.
546429907115.
55818230.
842319976165.
00352170.
645560837118.
88374210.
803475779159.
9105230.
734648608123.
67983260.
742813275153.
35904920.
795036187129.
80591790.
651920325148.
17322610.
835832231137.
13622190.
555455965144.
79312180.
870030478147.
0682390.
447830418119.
66556540.
900865679158.
81314350.
348424522116.
15846890.
922986443167.
42478470.
224790326112.
75154230.
937611403173.
16657360.
950916804178.
30306550.
961711466182.
90938680.
969500442186.
55900450.
975475075189.
95781350.
980606686193.
61003960.
983071645196.
04814080.
985545808198.
48823790.
987085227200.
43974950.
988505632202.
406399436FIGURE27–BETIsothermsforBio-MOF-1Seeds10012014016018020000.
10.
20.
30.
40.
50.
60.
70.
80.
91QuantityAdsorbed(cm3/gSTP)RelativePressure(P/Po)37TABLEIIIBETTABULARRESULTSFORBIO-MOF-1MEMBRANECRYSTALSRelativePressure(P/Po)QuantityAdsorbed(cm/gSTP)RelativePressure(P/Po)QuantityAdsorbed(cm/gSTP)0.
087852798198.
66603220.
988338981242.
98927460.
14363503202.
57105310.
969738226241.
04650450.
203083625205.
34800620.
945568241240.
22914910.
242925223206.
86536350.
921298621239.
75636440.
299893054208.
63390850.
886827064239.
16649890.
349428544210.
03133680.
875060839238.
93827720.
447333898212.
37010490.
841326532238.
22321950.
5463551214.
83141340.
801514808237.
40510020.
645386274218.
35242540.
74230533236.
20662590.
734584095224.
08747450.
653486106234.
04975560.
796981655229.
23554510.
553677834230.
5427630.
837959044232.
39437540.
450003981214.
78051570.
872440614234.
97878880.
351122259212.
11156870.
902568437237.
29272680.
224065469208.
55336490.
923440695238.
43987660.
93846468238.
93187470.
951426445239.
3699090.
962614722239.
90882760.
969947428240.
33265040.
975925209240.
85023150.
981046081241.
42524570.
98322796241.
78671350.
985230512242.
17867360.
987163304242.
65220960.
988338981242.
989274638FIGURE28-BETIsothermsforBio-MOF-1MembraneCrystals19020021022023024000.
10.
20.
30.
40.
50.
60.
70.
80.
91QuantityAdsorbed(cm3/gSTP)RelativePressure(P/Po)39VITANAME:JosephBohrmanADDRESS:DepartmentofChemicalEngineeringUniversityofLouisvilleLouisville,KY40292DOB:Paducah,KY–February14,1988EDUCATION&TRAINING:B.
S.
,ChemicalEngineeringUniversityofLouisville2006-11M.
Eng.
,ChemicalEngineeringUniversityofLouisville2011-12HONORS&AWARDS:HallmarkScholarship,UniversityofLouisville,2006-2011PROFESSIONALSOCIETIES:AmericanInstituteofChemicalEngineersTauBetaPiEngineeringSocietyNorthAmericanMembraneSociety